The present invention relates to the field of dimmer control systems for home and industrial lighting systems.
Various dimmer systems have been disclosed in the prior art for controlling power dissipation in a load. The simplest dimmer systems involve connection of a variable resistance in series or parallel with the load. These systems waste energy in I.sup.2 R heat losses in the variable resistance.
With the advent of solid state switching devices such as Triacs, other kinds of dimmer control systems have been devised. The most common of these systems involves switching of the Triac to the conductive state at some point on the waveform such that only a fraction of the complete waveform reaches the load. Power dissipation in the load in such systems depends upon how large a "piece" of the waveform is allowed to reach the load.
These prior art dimmer control systems suffer from several disadvantages. Principal among these disadvantages is radio frequency interference and audio noise. This noise is caused by transient phenomena generated when the power source is connected to the load at some point in the voltage waveform other than the zero crossing. These transients manifesting themselves as electrical noise represent wasted electrical energy.
Nonlinearity has also been a problem in these prior art systems in that many dimmer control systems will not begin to light the lamp until a point near the mid range of the dimmer control is reached.
Further, lamp life is shortened when surge currents caused by connection of the filaments to power sources near peaks in the voltage waveforms occurs. These same surge currents can overload current limiters in power supply circuits.
Accordingly, the present invention is directed to a dimmer control method and apparatus which effectively produces low noise, linear dimming control without transient surge currents. Radio frequency interference, audio noise, and transient surge currents are substantially eliminated by zero voltage switching. Linearity is improved because pre-programmed sequences of half-cycles are applied for any given setting of the dimmer control.
The dimmer control method and apparatus of the present invention is useful in home, theatrical, restaurant and many other commercial applications.
The present method and apparatus involves using a digital processor to sample the desired power dissipation setting of a dimmer control and then looking up a pre-programmed sequence of 0's and 1's for that setting in the processor's read only memory (ROM). Each setting of the dimmer control is converted by a dimmer data circuit to a pulse whose width reflects the setting of the dimmer control. The maximum setting of the dimmer control will be reflected in a pulse from the dimmer data circuit of a certain maximum width. Lesser settings result in lesser pulse widths. The digital processor periodically checks the setting of the dimmer control by sending a trigger pulse to the dimmer data circuit. This circuit then responds by sending a pulse of a width representative of the desired power dissipation setting back to the digital processor.
When this pulse from the dimmer data circuit arrives, the digital processor examines it to determine if the setting of the dimmer control has changed. This can be accomplished by counting the number of cycles of the digital processor's internal clock which occur while the dimmer data pulse is "high".
There is stored in a read only memory in the digital processor a separate bit sequence of 0's and 1's in the form of several multi-bit words for each of forty different power level settings of the dimmer control. If there are forty discrete levels, the sequences need be only forty bits long. For a given setting of the dimmer control, the digital processor cycles through each bit of each word in the bit sequence of 0's and 1's corresponding to that desired power level. The digital processor examines one bit of the sequence per each half cycle of the power supply waveform. If the digital processor finds a zero, it will not send a complete half cycle through the load. If it finds a one, then it will.
The inventor has recognized that the noise, surge current and nonlinearity problems of the prior art systems could be solved by using zero voltage switching and pre-programmed sequences of zeroes and ones in combination in a dimmer system. Intensity of the lamps can be controlled at low levels by merely adding more 1's to the sequence.
A zero voltage switch which is either a separate component or incorporated into the digital processor, sends a signal to the digital processor every time the power supply voltage waveform crosses zero. This signal tells the processor several things: first, how often to check the next location in the pre-programmed sequences; second, when to send an output trigger pulse to the Triac connected so as to connect the load with its power supply when the output trigger pulse is received. The Triac turns itself off at the next 0 crossing.